Effects of defects in Ga-doped ZnO nanorods formed by a hydrothermal method on CO sensing properties

This paper describes the synthesis of Ga-doped ZnO nanorods (NRs) by the hydrothermal (HT) method and the effects of Ga-doping on their CO sensing properties. It is found that Ga doping cancels oxygen-related defects (oxygen interstitial) based on results from X-ray diffraction (XRD) and photoluminescence (PL) experiments and further confirmed by a CO sensing experiment. The defects in ZnO NRs, which are both donor-related (shallow donor and zinc interstitial) and acceptor-related (oxygen interstitial), were dependent on the Ga doping level. The CO sensing properties of ZnO NRs are effectively improved by Ga doping, which likely results from the removal of excess oxygen on the ZnO NRs surface and increased shallow donor concentration. Ga-doped ZnO may be formed as an active component for CO absorption. The optimal 2% Ga-doped ZnO NRs based CO sensors showed a response factor of 25%, which was a 5-fold increase in sensitivity compared with the undoped devices, at the optimizing working temperature of 150 °C. The p–n junction-based sensors have a fast response as short as a few tens of seconds.